Effect of porcine stress syndrome on the solubility and degradation of myofibrillar/cytoskeletal proteins.

This study examined the effect of stress classification (stress-positive, stress-carrier, stress-negative) of pigs on selected properties of postmortem muscle, including protein solubility and degradation of proteins such as titin. Longissimus muscle samples were removed 45 min postslaughter, divided into samples, and stored at 0 to 2 degrees C for analysis at 0, 1, 3, 5, and 7 d postmortem. Whole-muscle samples (homogenates) and purified myofibrils were prepared from each sample for analysis by SDS-PAGE. A portion of each muscle sample also was extracted 1) with a low-ionic-strength solution to obtain a sarcoplasmic protein fraction and 2) with two different high-ionic-strength solutions to obtain a myofibrillar/cytoskeletal protein fraction for measurement of protein solubility and for analysis of extracts by SDS-PAGE. No significant differences were observed between muscle from stress-negative and stress-carrier animals in this study. Sarcoplasmic (P less than .05) and myofibrillar/cytoskeletal (P less than .01) protein solubility was lower in muscle samples from stress-positive animals than in muscle samples from stress-carrier and stress-negative animals at all postmortem times studied. The high molecular weight protein titin was degraded more slowly postmortem in muscle from stress-positive than in muscle from stress-negative animals, as observed by SDS-PAGE analysis of whole-muscle samples (homogenates) an myofibrils. The combination of lowered protein solubility and reduced rate of postmortem degradation of structural proteins such as titin may explain, at least in part, the reduced quality and protein functionality of muscle from stress-positive pigs.